The disclosure of Japanese Patent Application No. 2002-115336 filed on Apr. 17, 2002, including its specification, drawings, and abstract, is incorporated herein by reference in its entirety.
1. Field of Invention
The invention relates to an evaporative fuel treating device and method, and more particularly, to an evaporative fuel treating device and method for treating evaporative fuel generated in a fuel tank of an internal combustion engine without discharging it into the atmosphere.
2. Description of Related Art
According to the art related to the invention, an evaporative fuel treating device having a canister for adsorbing evaporative fuel generated in a fuel tank is known as disclosed, for example, in Japanese Patent Application Laid-Open No. 10-274106. This device has a mechanism that purges evaporative fuel adsorbed in the canister through the flow of air and a separating membrane that separates evaporative fuel from purge gas. Furthermore, this device has a condensing unit for liquefying evaporative fuel separated by the separating membrane and a recirculation path for recirculating the condensed fuel back into the fuel tank. The evaporative fuel treating device thus constructed allows evaporative fuel generated in the fuel tank to be treated in a closed system including the canister. Thus, the above-mentioned device of the related art makes it possible to effectively prevent evaporative fuel from being discharged into the atmosphere without necessitating complicated control such as correction of fuel injection amount.
As described already, the above-mentioned device of the related art extracts evaporative fuel from purge gas by means of a separating membrane. However, the currently available separating membrane does not allow evaporative fuel having a sufficiently high concentration to be taken out from purge gas purged from the canister. If fuel gas having a low concentration is directly recirculated into the fuel tank, various inconveniences are caused due to the influence of air contained in fuel gas. Hence, the above-mentioned device of the related art is designed such that the condensing unit for condensing fuel gas is disposed in a post stage of the separating membrane.
As described hitherto, the above-mentioned device of the related art cannot produce high-concentration fuel gas by means of the separating membrane and thus requires that the condensing unit be disposed in the post stage of the separating membrane.
It is one object of the invention to provide an evaporative fuel treating device that can sufficiently condense evaporative fuel only through a treatment by separating membranes and that makes recirculation of evaporative fuel to a fuel tank possible without employing a condensing unit.
An evaporative fuel treating device for an internal combustion engine in accordance with a first aspect of the invention comprises a canister that adsorbs evaporative fuel generated in a fuel tank and a purge pump that causes canister outlet gas to flow out from the canister. In addition, a separating unit separates the canister outlet gas into treating gas containing a high concentration of evaporative fuel, circulating gas containing a medium concentration of evaporative fuel, and canister inlet gas containing a low concentration of evaporative fuel. A treating gas passage introduces the treating gas from the separating unit into the fuel tank. A circulating gas passage causes the circulating gas to circulate from the separating unit to a location upstream of the separating unit. A canister inlet gas passage causes the canister inlet gas to circulate from the separating unit to a location upstream of the canister.
According to the above-mentioned first aspect, canister outlet gas purged from the canister can be separated into high-concentration treating gas, medium-concentration circulating gas, and low-concentration canister inlet gas by being treated by the separating unit. In this case, medium-concentration circulating gas is circulated back through the separating unit and is repeatedly subjected to a concentrating processing. Thus, the first aspect makes it possible to make the concentration of treating gas sufficiently high and the concentration of canister inlet gas sufficiently low. Treating gas having a sufficiently high concentration can be utilized as fuel by being introduced into the fuel tank. Canister inlet gas having a sufficiently low concentration can be utilized as gas for purging evaporative fuel adsorbed in the canister by being introduced into the canister. Thus, the first aspect makes it possible to ensure that evaporative fuel adsorbed in the canister can be efficiently utilized as fuel.
In the above-mentioned first aspect, it is preferable that the purge pump include a purge gas circulation pump that communicates with the canister, that the separating unit include a high-concentration separation unit and a medium-concentration separation unit. It is preferable that the high-concentration separation unit have a first separating membrane for separating gas containing evaporative fuel into high-concentration gas containing a high concentration of evaporative fuel and low-concentration gas containing a low concentration of evaporative fuel and separate mixed gas composed of the canister outlet gas and the circulating gas into the treating gas and medium-concentration gas. It also is preferable that the medium-concentration separation unit be disposed downstream of the high-concentration separation unit, have a second separating membrane functioning in the same manner as the first separating membrane, and separate the medium-concentration gas into the circulating gas and the canister inlet gas. In this construction, canister outlet gas can be produced by the purge gas circulation pump. Further, high-concentration treating gas, medium-concentration circulating gas, and low-concentration canister inlet gas can be produced from canister outlet gas by using the high-concentration separation unit and the medium-concentration separation unit.
In the above-mentioned aspect, it is preferable that an area of the first separating membrane be smaller than an area of the second separating membrane. In this construction, it becomes possible to efficiently take out high-concentration treating gas during treatment of mixed gas by the first separating membrane and to efficiently take out low-concentration canister inlet gas during treatment of medium-concentration gas by the second separating membrane, by making the area of the first separating membrane included in the high-concentration separation unit smaller than the area of the second separating membrane included in the medium-concentration separation unit.
In the above-mentioned aspect, it is preferable that a ratio between the area of the first separating membrane and the area of the second separating membrane be set such that the treating gas and the canister inlet gas contain evaporative fuel having a concentration equal to or higher than 95% and evaporative fuel having a concentration equal to or lower than 5% respectively in the case where canister outlet gas contains evaporative fuel having a concentration of 15%. In this construction, since the ratio between the area of the first separating membrane and the area of the second separating membrane assumes a suitable value, the concentration of evaporative fuel contained in treating gas and the concentration of evaporative fuel contained in canister inlet gas can be made equal to or higher than 95% and equal to or lower than 5% respectively if the concentration of evaporative fuel contained in canister outlet gas is equal to or higher than 15%. Hence, a processing of liquefying evaporative fuel in the canister can be continued until the concentration of canister outlet gas reaches 15%.
In the above-mentioned aspect, it is preferable that the evaporative fuel treating device further comprise a feed pump that feeds fuel in the fuel tank to the internal combustion engine, and that the treating gas passage introduce the treating gas into a fuel suction port of the feed pump. In this construction, treating gas can be introduced into the fuel suction port of the feed pump. Treating gas sucked into the feed pump is liquefied by being compressed therein. Thus, this aspect of the invention makes it possible to ensure that treating gas can be utilized as fuel without providing a special mechanism for liquefying treating gas.
In the above-mentioned aspect, it is preferable that the evaporative fuel treating device further comprise a venturi for generating a negative pressure at the fuel suction port of the feed pump. In this construction, treating gas can be smoothly sucked into the feed pump by providing the venturi at the fuel suction port of the feed pump.
In the above-mentioned aspect, it is preferable that the purge gas circulating pump be disposed between the canister and the high-concentration separation unit, and that the canister inlet gas passage be provided with a pressure-regulating valve that makes a pressure on the side of the medium-concentration separation unit higher than a pressure on the side of the canister. In this construction, the purge gas circulation pump is disposed between the canister and the high-concentration separation unit, and the pressure-regulating valve is disposed between the medium-concentration separation unit and the canister. A set pressure of the pressure-regulating valve is applied between the purge gas circulation pump and the pressure-regulating valve. The separating performances of the high-concentration separation unit and the medium-concentration separation unit are improved as pressures applied thereto are increased. Hence, they can exert excellent performances of treating evaporative fuel. The amount of canister inlet gas increases in proportion to a decrease in concentration of canister outlet gas, a decrease in amount of treating gas, and a decrease in amount of circulating gas. Hence, the smaller the amount of evaporative fuel in the canister becomes, the easier it becomes to create a state where the evaporative fuel is likely to be purged.
In the above-mentioned aspect, it is preferable that the evaporative fuel treating device be capable of making a treating performance at the time when the separating unit produces the treating gas variable, and that a controller of the device calculates a required amount of fuel to be treated, and controls the device on the basis of the required treatment amount. In this construction, the treating performance of the separating unit can be changed in accordance with a required amount of evaporative fuel to be treated. Thus, a suitable process of treating evaporative fuel can be performed in accordance with a state of the internal combustion engine.
In the above-mentioned aspect, the device can make a pressure of the mixed gas coming into contact with the first separating membrane and a pressure of the medium-concentration gas coming into contact with the second separating membrane variable, and the controller can increase the pressure in proportion to an increase in the required treatment amount. In this construction, a desired performance of treatment can be realized by changing the pressure of mixed gas coming into contact with the first separating membrane or the pressure of medium-concentration gas coming into contact with the second separating membrane.
In the above-mentioned aspect, a variable pressure-regulating valve can be used to make the pressure variable, and the controller increases the set pressure in proportion to an increase in the required treatment amount by adjusting the variable pressure-regulating valve. In this construction, a desired pressure can be created by changing the set pressure of the pressure-regulating valve.
In the above-mentioned aspect, the pressure can be varied by making a discharging performance of the purge gas circulation pump variable, and the controller increases the discharging performance of the purge gas recirculation pump in proportion to an increase in the required treatment amount. In this construction, a desired performance of treatment can be created by changing the discharging performance of the purge gas circulation pump.
In the above-mentioned aspect, the performance can be varied by using a canister heater that heats the canister. The controller increases an amount of heat to be generated by the canister heater in proportion to an increase in the required treatment amount. In this construction, a desired performance of treatment can be created by changing the degree to which the canister is heated.
In the above-mentioned aspect, the evaporative fuel treating device can include a negative pressure adjusting valve that is disposed between the canister and the purge gas circulation pump and that generates a negative pressure in the circulating gas passage during operation of the purge gas circulation pump. In this construction, a negative pressure can be generated in the circulating gas passage by disposing the negative pressure adjusting valve between the canister and the purge gas circulation pump. The negative pressure generated in the circulating gas passage is applied to the second separating membrane and increases a differential pressure that is applied across the second separating membrane. Thus, this aspect of the invention makes it possible to generate a high differential pressure without applying an excessively high positive pressure to the second separating membrane, and to cause the medium-concentration separation unit to exert an excellent performance of concentration.
In the above-mentioned aspect, it also is preferable that the evaporative fuel treating device further include desorption promoting means for promoting desorption of evaporative fuel from the canister. In this construction, since the desorption promoting means for promoting desorption of evaporative fuel from the canister is provided, evaporative fuel in the canister can be suitably purged despite the fact that evaporative fuel is contained in canister inlet gas.
In the above-mentioned aspect, the desorption promoting means can include a canister heater that heats the canister. In this construction, desorption of evaporative fuel can be effectively promoted by heating the canister.
In the above-mentioned aspect, it is possible that the canister and the purge gas circulation pump be disposed such that heat resulting from operation of the purge gas circulation pump is transmitted to the canister, and that the canister heater include the purge gas circulation pump. In this construction, the canister can be heated utilizing heat generated by the purge gas circulation pump. Alternatively, or in addition, a dedicated heater can be provided for the canister.
In the above-mentioned aspect, the evaporative fuel treating device can further comprise a concentration detector that detects at least one of a concentration of the canister outlet gas, a concentration of the mixed gas, and a concentration of the treating gas, and the controller determines, on the basis of a difference between a value detected by the concentration detector during operation of the desorption promoting means and a value detected by the concentration detector during stoppage of the desorption promoting means, whether or not the desorption promoting means is functioning abnormally. In this construction, it is possible to determine, by comparing a concentration indicating a state of desorption of evaporative fuel from the canister (a concentration of canister outlet gas or the like) during operation of the desorption promoting means with a concentration indicating a state of desorption of evaporative fuel from the canister (a concentration of canister outlet gas or the like) during stoppage of the desorption promoting means, whether or not the desorption promoting means is functioning properly, namely, whether or not there is an abnormality occurring in the desorption promoting means.
In the above-mentioned aspect, it is preferable that the high-concentration separation unit be disposed below the medium-concentration separation unit. In this construction, since the high-concentration separation unit is disposed below the medium-concentration separation unit, it is possible to efficiently ensure that high-concentration gas, which has a greater specific gravity, exists in the high-concentration separation unit. Thus, this aspect of the invention makes it possible to ensure a high performance of treatment.
In the above-mentioned aspect, it is preferable that the fuel tank be disposed below the high-concentration separation unit and the medium-concentration separation unit. In this construction, since the fuel tank is disposed below the high-concentration separation unit and the medium-concentration separation unit, fuel that has been liquefied in the units can be efficiently returned to the fuel tank.
In the above-mentioned aspect, it is preferable that the evaporative fuel treating device further includes a concentration detector that detects at least one of a concentration of the canister outlet gas, a concentration of the mixed gas, and a concentration of the treating gas, and that the ratio between an area of the first separating membrane and an area of the second separating membrane be variable. It is preferable that the controller controls the variable area ratio on the basis of a value detected by the concentration detector. In this construction, a suitable performance of treating evaporative fuel can be realized in accordance with a state of the canister by changing an area ratio between the first and second separating membranes in accordance with a concentration indicating a state of desorption of evaporative fuel from the canister (a concentration of canister outlet gas or the like).
In the above-mentioned aspect, it is preferable that the high-concentration separation unit be provided with a plurality of treating chambers, that the first separating membrane include a plurality of portions each of which separates a corresponding one of the treating chambers into a corresponding one of upper chambers and a corresponding one of lower chambers, that the treating chambers be arranged such that the upper chambers lead to one another in series and that all the lower chambers communicate with the treating gas passage. The variable area ratio can be varied by including at least two passages for introducing the mixed gas into at least two of the upper chambers respectively and a valve mechanism that makes a ratio between amounts of the mixed gas flowing through the at least two passages variable. The controller controls the valve mechanism on the basis of a value detected by the concentration detector. In this construction, the area ratio between the first and second separating membranes can be substantially changed by changing the amount of mixed gas flowing through the upper chambers included in the high-concentration separation unit or the like.
In the above-mentioned aspect, it is preferable that the evaporative fuel treating device further comprise a treating gas tank that communicates with the treating gas passage and that accumulates the treating gas and fuel gas supply that supplies the internal combustion engine with fuel, that is, the treating gas accumulated in the treating gas tank when the internal combustion engine is started. In this construction, startability of the internal combustion engine can be enhanced by utilizing treating gas accumulated in the treating gas tank as fuel when the internal combustion engine is started.
In the above-mentioned aspect, it is preferable that the evaporative fuel treating device further comprise a pump outlet pressure detector that detects a pressure applied to an outlet portion of the purge gas circulation pump, and the controller recognizes the occurrence of an abnormality in the purge gas circulation pump or in a path extending from the purge gas circulation pump to the pressure-regulating valve if the pressure that is applied to the outlet portion and that has been detected under circumstances requiring the purge gas circulation pump to be operated is unequal to a predetermined value. In this construction, in the case where the purge gas circulation pump is required to operate, it is possible to determine, depending on whether or not there is a suitable pressure at the outlet portion of the pump, whether or not the pump is operating properly and whether or not there is an abnormality in the path extending from the pump to the pressure-regulating valve.
In the above-mentioned aspect, it is preferable that the evaporative fuel treating device further comprise a pump outlet pressure detector that detects a pressure applied to the outlet portion of the purge gas circulation pump, and the controller determines, on the basis of a pressure change that occurs in the outlet portion immediately after operation of the purge gas circulation pump has been stopped, whether or not leakage has been caused in the path extending from the purge gas circulation pump to the pressure-regulating valve. In this construction, it is possible to determine, depending on whether or not the pressure at the outlet portion of the purge gas circulation pump suitably changes after stoppage thereof, whether or not leakage has been caused in the path extending from the pump to the pressure-regulating valve.
In the above-mentioned aspect, it also is preferable that the evaporative fuel treating device further comprise a canister flow gas detector that detects a flow rate of gas flowing through the canister, and the controller makes, on the basis of a flow rate of gas flowing through the canister, a determination on completion of operation of the purge pump. In this construction, it is possible to make a determination on completion of purge on the basis of a flow rate of gas flowing through the canister. The flow rate of gas increases as the flow rates of treating gas and circulating gas decrease in response to a decrease in amount of evaporative fuel in the canister. Thus, purge can be completed as soon as evaporative fuel in the canister is suitably treated.